fn main() {
    let mut x = 5;
    println!("The value of x is: {}", x);
    x = 6;
    println!("The value of x is: {}", x);
    let x = x + 1;
    {
        let x = x * 2;
        println!("The value of x in the inner scope is: {}", x);
    }
    println!("The value of x is: {}", x);

    const THREE_HOUR_IN_SECONDS: u32 = 3 * 60 * 60;
    println!("The value of THREE_HOUR_IN_SECONDS is: {}", THREE_HOUR_IN_SECONDS);
    // const 定义的常量是不可被遮蔽的
    // const THREE_HOUR_IN_SECONDS: u32 = 1 * 60 * 60;
    // println!("The value of THREE_HOUR_IN_SECONDS is: {}", THREE_HOUR_IN_SECONDS);

    // let 定义的变量方可进行遮蔽（shadow）
    let x = 11;
    println!("The value of x is: {}", x);
}
